1. Field of the Invention
This invention relates to seals and, more particularly, a sealing mechanism for communicating high vacuum onto rotating machinery having virtually unlimited rotation.
2. Background
High vacuum is defined as having a pressure of less than 0.001 millimeters (mm) of mercury. When using rotating machinery, such as a centrifuge, there is occasionally a need to transmit high vacuum onto the rotating/moving components. For example, there are engineering applications where it is critical to deliver and maintain high vacuum to a component rotating at a relatively high speed for extended periods of time. One such application involves a centrifuge which accelerates small-scale models to simulate and study civil engineering problems. In these simulations, rotation of a model or component may be required at speeds of four (4) revolutions per second for periods ranging from several hours to several days. At the same time, it may be necessary to maintain vacuum levels ranging from 0.001 to 0.00000145 mm of mercury while the rotating component experiences essentially unlimited angular displacement. Presently, no technology exists to satisfactorily provide for such requirements.
Currently, there are various rotating seals used to transmit high vacuum onto rotating/moving components. For example, rotating seals may be constructed of metal surfaces which are mated by swaging. Alternatively, rotating seals may be constructed of soft lubricated polymeric surfaces (such as rubber or plastic) which are held in forced contact by pressure. With either type of rotating seal, excessive friction has been a problem. Frictional forces cause rapid wear of the seal which compromises its integrity and results in vacuum leakage. Further, frictional forces may generate undesirable heat. Accordingly, in the case of either swaged metal seals or lubricated polymeric seals, only a limited amount of rotation is possible before the sealing surfaces are worn and damaged.
Rotary slip-rings are sometimes used as an alternative to rotating seals; however, slip-rings are not designed to transmit vacuum. Instead, slip-rings transmit positive pressures where leakage is much less critical. In fact, slip-rings are not leak-tight and therefore will not allow high levels of vacuum to be maintained.
Accordingly, there is no presently available seal technology which provides a sufficient seal for the transmission of high vacuum onto rotating machinery wherein,the seal has the ability to accommodate unlimited rotation. There is a further need for a seal which is constructed of materials that do not fatigue or wear and which offers minimal frictional resistance to rotary motion while simultaneously generating negligible heat during operation.